本文關(guān)鍵詞：多鐵異質(zhì)結(jié)中的磁電耦合和電阻轉(zhuǎn)換效應(yīng)　出處：《中國(guó)科學(xué)技術(shù)大學(xué)》2016年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 多鐵材料 磁電耦合效應(yīng) 異質(zhì)結(jié) 磁介電效應(yīng) 鐵電性 電阻轉(zhuǎn)換效應(yīng) 界面效應(yīng)

【摘要】：隨著自旋電子學(xué)／電子學(xué)過(guò)去數(shù)十年的迅猛發(fā)展,人們對(duì)器件的小型化、器件的讀寫速度以及其讀寫能耗都有了更高的要求。然而,現(xiàn)有的技術(shù)與材料已經(jīng)到達(dá)其尺寸和性能的極限,并開始制約電子器件科學(xué)的發(fā)展�！虼颂剿髂軌驖M足生產(chǎn)生活更高要求的新材料進(jìn)而變革電子器件領(lǐng)域變得尤為迫切和重要。具有多功能的、可進(jìn)行多參量調(diào)控的多鐵材料受到了科學(xué)家們的廣泛關(guān)注。多鐵材料以其鐵電極化和磁極化共存、磁電間可相互耦合調(diào)控而有望在多功能電子器件革新上發(fā)揮巨大的作用。然而,目前室溫單相的多鐵性材料匱乏且磁電耦合效應(yīng)弱,可以進(jìn)行人工設(shè)計(jì)的復(fù)合多鐵性材料——多鐵異質(zhì)結(jié)由于其在材料選擇和磁電耦合效應(yīng)方面都有著巨大的優(yōu)勢(shì)而引起了廣泛地關(guān)注。目前盡管在多鐵異質(zhì)結(jié)磁電耦合方面已經(jīng)取得了一定的研究進(jìn)展,但其中仍然存在大量的、與實(shí)際生產(chǎn)應(yīng)用密切相關(guān)的問(wèn)題,比如如何在室溫甚至高溫條件下實(shí)現(xiàn)強(qiáng)烈的磁電耦合效應(yīng)、異質(zhì)結(jié)中的磁性層對(duì)異質(zhì)結(jié)整體在磁場(chǎng)下的介電鐵電性的影響有多大,如何成功地將疇壁工程和宏觀電輸運(yùn)性質(zhì)緊密聯(lián)系在一起實(shí)現(xiàn)更多的電阻狀態(tài)等等。針對(duì)上述問(wèn)題,本論文主要研究了磁性電極材料對(duì)多鐵異質(zhì)結(jié)中的磁電耦合效應(yīng)和介電／磁介電效應(yīng)的影響：探討了多鐵異質(zhì)結(jié)中界面效應(yīng)和鐵電疇壁同時(shí)參與的三阻態(tài)阻變效應(yīng)的起源,為多重態(tài)存儲(chǔ)器件的原型設(shè)計(jì)提供了一定的思路。整篇論文分為六個(gè)章節(jié),每一章的主要內(nèi)容可概括如下：在第一章中,綜述了單相多鐵材料的多鐵性起源以及復(fù)合多鐵材料的優(yōu)勢(shì),重點(diǎn)介紹了磁介電效應(yīng)和多鐵異質(zhì)結(jié)中磁電耦合效應(yīng)以及相關(guān)研究進(jìn)展,最后簡(jiǎn)單介紹了多鐵性異質(zhì)結(jié)相關(guān)的電阻轉(zhuǎn)換效應(yīng)并對(duì)其中的機(jī)理進(jìn)行了闡述。在第二章中,為了研究磁性電極電阻對(duì)外延的BiFeO3/La0.625Ca0.375MnO3 (BFO/LCMO)異質(zhì)結(jié)鐵電性的影響,我們利用不同的電極配置系統(tǒng)地測(cè)量了BFO/LCMO異質(zhì)結(jié)的鐵電性,發(fā)現(xiàn)表觀矯頑電壓隨著LCMO電阻線性增加。通過(guò)建立分壓模型,去除了來(lái)自于LCMO層的分壓的非本征效應(yīng),進(jìn)而得到了異質(zhì)結(jié)本身的矯頑電壓Vac0,同時(shí)我們發(fā)現(xiàn)當(dāng)溫度高于150 K時(shí),Vac0同樣的對(duì)磁場(chǎng)有明顯的響應(yīng),顯示出本征磁電耦合效應(yīng)。實(shí)驗(yàn)結(jié)果證明,對(duì)于鐵電／鐵磁復(fù)合薄膜來(lái)說(shuō),當(dāng)研究異質(zhì)結(jié)本身的鐵電性時(shí),鐵磁層的分壓作用不可忽視；同時(shí)提供了一種有效的、定量的方式來(lái)分析LCMO層在多層異質(zhì)結(jié)薄膜上的分壓貢獻(xiàn),這對(duì)研究鐵電／鐵磁異質(zhì)結(jié)的本征磁電耦合效應(yīng)以及相關(guān)器件設(shè)計(jì)很有幫助。在第三章中,為了研究磁性電極電阻對(duì)外延BFO/LCMO異質(zhì)結(jié)介電性的影響,我們利用不同的電極配置,系統(tǒng)地測(cè)量了Au/BFO/LCMO異質(zhì)結(jié)的介電性能,發(fā)現(xiàn)隨著LCMO底電極電阻的增加,Au/BFO/LCMO多鐵異質(zhì)結(jié)電容的實(shí)部有明顯的降低,且體系弛豫行為所對(duì)應(yīng)的頻率均向高頻移動(dòng)。通過(guò)分析異質(zhì)結(jié)介電損耗隨溫度的依賴關(guān)系,發(fā)現(xiàn)參與介電測(cè)量的底電極LCMO所占比例越多,異質(zhì)結(jié)的磁介電效應(yīng)也越大,但損耗tan δ的值也越大。通過(guò)研究不同電極配置下異質(zhì)結(jié)電容虛部隨頻率的變化規(guī)律,發(fā)現(xiàn)對(duì)于任意的電極配置,異質(zhì)結(jié)的介電弛豫行為主要可等效地反映出Mn3+和Mn4+之間的電子躍遷或轉(zhuǎn)移過(guò)程。上述發(fā)現(xiàn)對(duì)研究鐵電／鐵磁異質(zhì)結(jié)的磁介電效應(yīng)是很有幫助的,同時(shí)可以對(duì)相關(guān)器件設(shè)計(jì)有一定的指導(dǎo)作用在第四章中,我們通過(guò)電感耦合等離子質(zhì)譜儀(ICP-MS)判斷出所生長(zhǎng)的BFO薄膜中不存在Bi元素的缺失,這對(duì)分析半導(dǎo)體性質(zhì)的BiFeO3的半導(dǎo)體類型以及在Au/BiFe03/La0.6Sr0.4Mn03 (Au/BFO/LSMO)多鐵異質(zhì)結(jié)中界面肖特基勢(shì)壘的方向起到關(guān)鍵性作用；利用掃描透射電子顯微鏡(STEM)對(duì)異質(zhì)結(jié)上下界面的晶體結(jié)構(gòu)進(jìn)行了細(xì)致的表征,在BFO/LSMO界面處發(fā)現(xiàn)了存在明顯離子互擴(kuò)散區(qū)域的中間過(guò)渡層,在Au/BFO界面處觀察到了"dead layer ".上述發(fā)現(xiàn)為后續(xù)分析異質(zhì)結(jié)阻變行為起源奠定了堅(jiān)實(shí)的實(shí)驗(yàn)基礎(chǔ)。在第五章中,我們研究了Au/BFO/LSMO多鐵異質(zhì)結(jié)中電磁調(diào)控的可重復(fù)、區(qū)分度較高的三阻態(tài)行為。通過(guò)改變鐵電極化的方向,異質(zhì)結(jié)的電阻可以在三種穩(wěn)定非易失的電阻狀態(tài)之間切換且不需要電形成過(guò)程。這種非易失的電阻轉(zhuǎn)換行為可以被歸結(jié)以下三個(gè)方面的共同作用：Au/BFO界面處的肖特基勢(shì)壘高度的變化、BFO/LSMO的界面電阻大小的變化以及BFO鐵電疇壁密度相關(guān)的電阻改變。使用異質(zhì)結(jié)矯頑電壓附近的脈沖電壓極化樣品后所觀察到的具有最高電導(dǎo)率的第三態(tài)在室溫下表現(xiàn)出明顯負(fù)磁阻效應(yīng),通過(guò)宏觀電測(cè)量證明了BFO鐵電疇壁在室溫下的負(fù)磁阻效應(yīng)。以上的發(fā)現(xiàn)對(duì)我們深入理解多鐵異質(zhì)結(jié)中的界面效應(yīng)以及鐵電疇壁的鐵磁性對(duì)非易失電阻轉(zhuǎn)換效應(yīng)的影響,使得將自旋電子學(xué)引入阻變存儲(chǔ)器件成為可能。在第六章中,我們?cè)诓煌瑔尉бr底上生長(zhǎng)了Co薄膜,研究了其中磁各項(xiàng)異性,發(fā)現(xiàn)對(duì)于所研究的幾種單晶襯底上的Co薄膜而言,均滿足易磁化軸方向上的電阻大于難磁化軸方向上的電阻這一規(guī)律。但是,各項(xiàng)異性磁阻對(duì)外加磁場(chǎng)和方向的依賴關(guān)系有待進(jìn)一步的研究和探索。
[Abstract]:Over the past few decades with the rapid development of spintronics / electronics, people for miniaturization of devices, devices to read and write the read and write speed and energy consumption have a higher demand. However, the ultimate technology and existing materials has reached its size and performance, and began to restrict the development of electronic science. "Therefore to explore the production of new materials to meet the higher requirements of the life and change the field of electronic devices has become particularly urgent and important. With multi functions, multiferroic materials can be multi parameter regulation is widely concerned by scientists. Many iron materials to the ferroelectric polarization and magnetic polarization coexist between the coupling and magnetoelectric is expected to play a big role in the innovation of functional electronic devices. However, the current room temperature single-phase multiferroic material shortage and magnetoelectric coupling in multiferroic composite can be weak, artificial design Materials -- iron heterojunction due to the material selection and the magnetoelectric effect have a huge advantage and has aroused wide concern. Although the magnetoelectric coupling in multiferroic heterogeneous node has made some progress. But there are still a lot of closely related with the practical application problems, such as how to realize the strong magnetoelectric effect at room temperature even under high temperature conditions, the magnetic layer heterojunction in heterojunction under magnetic field affects the overall dielectric ferroelectric is, how successfully the domain wall engineering and macro electrical transport properties closely together to achieve more resistance and so on. In view of the above the problem, this paper mainly studied the influence of magnetic electrode materials on the magnetoelectric coupling in multiferroic heterostructures and dielectric / magnetic dielectric effect: To investigate the effect of multiferroic interface and heterostructure The origin of the three resistance state resistance domain wall also participates in effect, provide some ideas for the prototype design of multiple state memory devices. The whole thesis is divided into six chapters, the main contents of each chapter are summarized as follows: in the first chapter, this paper reviews the origin of iron multiferroic materials and the advantages of composite multiferroic materials, focuses on the progress of the magnetoelectric effect magnetodielectric effect and multiferroic heterostructure and related research, finally introduces the multiferroic heterostructures the resistance switching effect and the mechanism is also discussed. In the second chapter, in order to study the magnetic resistance of the electrode on the extension of the BiFeO3/La0.625Ca0.375MnO3 (BFO/LCMO) ferroelectric heterojunction effect, we use different electrode configurations to systematically measure the ferroelectric properties of BFO/LCMO heterojunction, found that the apparent coercive voltage with resistance linear increase. By LCMO To establish the model of partial pressure, removed from the LCMO layer of the partial pressure of the extrinsic effect, then obtained the heterojunction itself coercive voltage Vac0, we also found that when the temperature is higher than 150 K, Vac0 had the same response to magnetic field shows the inherent magnetoelectric coupling effect. The experimental results show that the for the ferroelectric / ferromagnetic composite film, when the ferroelectric heterojunction itself when the effect of ferromagnetic layer pressure can not be ignored; but also provides an effective and quantitative method to analyze the LCMO layer in the multilayer heterostructure thin films on partial pressure contribution, which is very helpful to the intrinsic magnetoelectric the coupling effect of ferroelectric / ferromagnetic heterojunction devices and related design. In the third chapter, in order to study the influence of magnetic electrode resistance on the dielectric properties of the epitaxial growth of BFO/LCMO heterojunction, we use different electrode configurations, system measurement Au/BFO/LCMO heterojunction The dielectric properties, it is found that with the increase of LCMO bottom electrode resistance, real Au/BFO/LCMO iron heterojunction capacitance is obviously reduced, and the corresponding system of relaxation frequency move to high frequency. Through the analysis of heterojunction dielectric loss with temperature dependence, found in the bottom electrode dielectric measurement by LCMO the proportion of the more magnetic dielectric effect of heterojunction is larger, but the loss of Tan 8 increased. Through the configuration of different electrode heterojunction imaginary capacitance changes with the frequency, for arbitrary electrode configuration, heterojunction dielectric relaxation behavior can reflect the electronic equivalent the transition or transfer process between Mn3+ and Mn4+. These findings are helpful to the study of ferroelectric / ferromagnetic heterojunction magneto dielectric effect, also can have a certain guiding role in the fourth chapter of the relevant device design, we through the inductor Coupled plasma mass spectrometry (ICP-MS) deletion of the Bi element does not exist out of the growth of the BFO thin film, the semiconductor type analysis of semiconductor properties of BiFeO3 and Au/BiFe03/La0.6Sr0.4Mn03 (Au/BFO/LSMO) - iron heterojunction interface in the direction of Schottky barrier plays a key role; by scanning transmission electron microscopy (STEM) on the crystal the structure of the interface under the heterojunction was characterized in detail, the obvious ion diffusion transition layer region is found at the interface of BFO/LSMO and Au/BFO in the interface is observed at the "dead layer". The findings for the subsequent analysis of heterojunction resistive behavior origin has laid a solid basis for experiment in Chapter fifth. Au/BFO/LSMO, we study the electromagnetic control multiferroic heterostructure can be repeated to distinguish the three resistance behavior of high degree. By changing the polarization direction of ferroelectric heterostructures, resistance In three kinds of non stable process between the resistance state of volatile switching and does not need electricity. This non volatile resistance switching behavior can be attributed to the following three aspects: the interface of Au/BFO Schottky barrier height changes, BFO/LSMO interface resistance changes in the size and resistance of BFO ferroelectric domain wall density the change of use. Near the heterojunction coercive voltage pulse voltage polarization samples observed after the third state has the highest conductivity at room temperature showed significant negative magnetoresistance effect, through the macroscopic electrical measurements demonstrated that the negative magnetoresistance effect of BFO ferroelectric domain wall at room temperature. The result of in-depth understanding of the interface effects of excess iron the heterojunction and ferromagnetic ferroelectric domain wall of nonvolatile resistive switching effect on us, which will introduce spintronics resistive memories become possible in sixth. In Chapter one, we grow Co films on different substrates, on which magnetic anisotropy, it is found that for Co single crystal substrate of several film on, meet the resistance of the easy axis direction is greater than the resistance of hard axis in the direction of the law. However, the anisotropic magnetoresistive foreign dependence the magnetic field and the direction of the need for further research and exploration.

【學(xué)位授予單位】：中國(guó)科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：O482.51
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本文編號(hào)：1410799